1. Field of the Invention
The present invention relates to a process for the preparation of cyclohexanone and cyclohexanol by hydrogenation of phenol in the gas phase over palladium on supports, which is characterized in that particular ratios of cyclohexanone to cyclohexanol can be established in a controlled manner as required by specific treatment of the catalysts during activation and regeneration.
2. Description of the Related Art
As is known, cyclohexanol is chiefly used for the preparation of adipic acid and cyclohexanone is essentially used for the synthesis of caprolactam. The two starting products in turn can be obtained by hydrogenation of phenol. If adipic acid and caprolactam production are to be supplied by this route and the two have varying capacities, it is necessary either to hydrogenate phenol exclusively to give cyclohexanol, which is achieved, for example, with certain nickel catalysts (compare Ullmann's Encyclopedia Vol. A8, page 218; DD 224315-A and DD 281079-A) and then to dehydrogenate some of the cyclohexanol, for example with catalysts of Cu, Zn or Cr (compare Ullmann's Encyclopedia Vol. A8, page 221; Chem. and Ind. 1989, page 832 and Chem. Techn. 18 (1966), page 611), or some of the phenol is hydrogenated over nickel catalysts to give cyclohexanol and another portion is hydrogenated over palladium catalysts to give cyclohexanone. Such a procedure is described, inter alia, in Chem. and Ind. 1989, page 832. In each case, two different catalysts and two plants suitable for this purpose are required.
The object was thus to prepare the two starting substances, cyclohexanone and cyclohexanol, in predetermined but variable proportions as required over only one catalyst and in only one plant.